Method for active and centralised ballasting of a semi-submersible float for an offshore wind turbine and float

Abstract

The invention relates to a method for the active and centralised ballasting of a semi-submersible float (2) for an offshore wind turbine, the float comprising at least four columns, including a central column (4) and three outer columns (6), which are connected to the central column by lower arms forming pontoons (8), wherein the method comprises the controlled and centralised displacement of a ballast fluid between sealed compartments (14) formed inside each pontoon (8), so as to modify the inclination thereof. The invention also relates to a semi-submersible float for an offshore wind turbine with active and centralised ballasting.

Description

Description Title of the invention: Method for active and centralized ballasting of a semi-submersible float for offshore wind turbine and float Technical Field

[0001] The present invention relates to the general field of semi-submersible floats used for offshore wind turbines.

[0002] More specifically, it concerns a ballasting process for such a float, as well as a semi-submersible float for an offshore wind turbine with active and centralized ballasting. Prior art

[0003] An offshore wind turbine uses wind energy to generate electricity using a turbine and an electric generator. There are two main types of offshore wind turbines: fixed wind turbines, which are installed on the seabed (at shallow depths, typically less than 50m), and floating wind turbines, which offer the advantage of being able to be built on land and installed in areas where the seabed depth typically exceeds 50m.

[0004] The floating wind turbines to which the present invention relates comprise a turbine generally formed by a motor with several horizontal-axis rotating blades and an electric generator coupled to the motor, the motor and the generator being fixed to an upper end of a vertical mast (or pylon). The lower end of the mast is mounted on a floating support structure (hereinafter referred to as a float).

[0005] There are several main families of floats for offshore wind turbines: semi-submersible floats, submerged floats with tensioned cables (or "TLP" platforms for "Tension-Leg Platform" in English), "SPAR" type floats (for "Single Point Anchor Reservoir"), semi-submersible "barge" type floats, and floats with a pendulum counterweight.

[0006] The invention relates more specifically to semi-submersible floats, i.e. steel or concrete foundations which generally take the form of a tripod with three (or four) cylindrical columns connected to each other by metal structures. The stability of the structure is ensured by a ballasting system which allows part of the foundation to be submerged. This structure is characterized by its large size and reduced draft.

[0007] For example, we can refer to publication FR 3,064,973 which describes a semi-submersible hybrid float structure comprising a central column and three external columns connected to the central column by pontoon-shaped branches.

[0008] Reference may also be made to publications FR 2,079,204 and WO 2018 / 197644 which describe semi-submersible float structures equipped with a passive ballast system.

[0009] These types of floats have the advantage of being simple in design. However, these floats do not have an active ballasting system. The general objective of active ballasting is to move quantities of fluid to and from different watertight compartments of the float in order to correct the float's inclination during operating phases. This limits the inclination of the turbine tower in order to increase energy production and reduce loads due to the inclination of the tower. Statement of the invention

[0010] There is therefore a need to be able to have a semi-submersible float equipped with active ballasting.

[0011] According to the invention, this aim is achieved by means of a method for active and centralized ballasting of a semi-submersible float for an offshore wind turbine, the float comprising at least four columns including a central column and three external columns connected to the central column by lower branches forming pontoons, the method comprising the controlled and centralized movement of a ballasting fluid between watertight compartments formed inside each pontoon so that their inclination can be modified.

[0012] The active ballasting method according to the invention makes it possible to reduce the total weight of the float by reducing fatigue loads. It also makes it possible to reduce the overall dimensions of the float, which facilitates access to certain ports and means of dry transport. The method according to the invention also makes it possible to increase the energy production of the turbine by reducing the inclination of the mast that supports it.

[0013] The movement of ballast fluid can be achieved between compartments located inside one longitudinal end of each pontoon on the outer column side.

[0014] Additionally, the method may further comprise moving a ballast fluid between additional sealed compartments located at hydrodynamic damping plates positioned around at least a portion of the outer columns.

[0015] The invention also relates to a semi-submersible float for an offshore wind turbine with active and centralized ballasting, comprising at least four columns including a central column and three external columns connected to the central column by lower branches forming pontoons, each pontoon comprising at least one watertight compartment forming a ballast zone, the float further comprising means for moving a ballast fluid in a controlled and individual manner between the compartments of the float so as to be able to modify the inclination of the float.

[0016] Each pontoon may include a compartment located at one longitudinal end on the outer column side, the compartments being connected to each other by a network of pipes coupled to a network of pumps.

[0017] Additionally, the float may further comprise additional watertight compartments located at hydrodynamic damping plates positioned around at least a portion of each outer column, the compartments being connected to each other by a network of pipes coupled to the network of pumps.

[0018] Preferably, the pump network is positioned inside the central column in the lower part thereof.

[0019] The float pontoons are each advantageously formed by an assembly of flat panels and each have a polyhedral cross-section.

[0020] In this case, the outer columns may each be a cylindrical shape. Alternatively, the outer columns may each be formed by an assembly of flat panels and each have a polyhedral cross-section.

[0021] Preferably, the flat panels of each pontoon are assembled together at edges which extend longitudinally between two columns and which are rounded by connecting at each of their longitudinal ends to a column by means of a transition piece.

[0022] The central column of the float may have a truncated cone shape. Alternatively, the central column may have a polyhedral shape.

[0023] The invention also relates to an offshore wind turbine comprising a float as defined above. Brief description of the drawings

[0024] [Fig. 1] Figure 1 represents in perspective a semi-submersible float according to an embodiment of the invention

[0025] [Fig. 2] Figure 2 is a view of Figure 1 in section plane II.

[0026] [Fig. 3] Figure 3 is a perspective view of Figure 2.

[0027] [Fig. 4] Figure 4 is a sectional view in a horizontal plane of the float of Figure 1.

[0028] [Fig. 5] Figure 5 is a sectional view in the height direction of a semi-submersible float according to another embodiment of the invention. Description of the embodiments

[0029] Figure 1 represents in perspective a semi-submersible float 2 for an offshore wind turbine according to a first embodiment of the invention.

[0030] In this embodiment, the float 2 comprises four vertical columns including a central column 4 intended to receive a wind turbine mast (not shown in FIG. 1), and three external columns 6 which are connected to the central column 4 by branches forming lower pontoons 8.

[0031] More specifically, the lower pontoons 8 and the outer columns 6 are angularly spaced from each other by 120° to form a star structure.

[0032] Furthermore, at least the pontoons formed by a plurality of flat panels which are assembled together. More precisely, in the embodiment of FIG. 1, each lower pontoon 8 is constituted by the assembly of four flat panels 81 to 8 4 forming a rectangular parallelepiped (only flat panels 81 and 8 4 are visible in Figure 1).

[0033] Of course, it is possible to consider that the number of flat panels forming each pontoon is different (for example five, six, etc.).

[0034] Preferably, the flat panels of each pontoon are assembled together at edges 10 which extend longitudinally between two columns and which are rounded by connecting at each of their longitudinal ends to a column by means of a transition piece 12.

[0035] The rounded edges 10 of the pontoons are connected at each of their two longitudinal ends to a vertical column of the float by means of a transition piece 12 making it possible to change from a quarter-circle shape to a right-angle shape.

[0036] It will be noted that in the embodiment of Figure 1, the outer columns 6 of the float 2 each have a substantially cylindrical shape. Of course, the invention also applies to floats whose outer columns are each formed by an assembly of flat panels in order to have a polyhedron shape (reference may be made to patent application FR 23 01328 filed on February 13, 2023 by the Applicant).

[0037] It will also be noted that in the embodiment of Figure 1, the central column 4 of the float 2 receiving the wind turbine mast has the shape of a truncated cone widening downwards. Of course, the invention also applies to floats whose central column has a cylindrical shape.

[0038] Furthermore, in the embodiment of the invention shown in Figures 2 to 4, each lower pontoon 8 of the float contains a watertight internal compartment 14 forming a ballast zone which is located at a longitudinal end of the pontoon on the outer column 6 side.

[0039] Furthermore, these watertight compartments 14 are connected to each other by a network of pipes 16 coupled to a network of pumps 18 advantageously located inside the central column 4 of the float in the lower part thereof.

[0040] As shown in Figures 2 and 3, these compartments 14 can extend over the entire width and height of the pontoons 8 and are delimited longitudinally by two watertight partitions 14a. A pipe 16 opens into the space delimited longitudinally between these two watertight partitions 14a.

[0041] A control system (not shown in the figures) makes it possible to control the network of pumps 18 in order to move ballast fluid (typically water, and in particular sea water) between the different compartments 14 of the float so as to correct the inclination of the float during the operating phases (typically of the order of 0 to 3°).

[0042] To achieve such a correction of the float inclination, it is generally necessary to move between 100 and 500 tonnes of ballast fluid between the different compartments of the float.

[0043] Figure 5 shows another embodiment of the invention in which the float 2' further comprises (compared to the float of the embodiment of Figures 1 to 4) hydrodynamic damping plates 20 which are positioned around at least a portion of the outer columns 6 at the lower portion thereof.

[0044] These hydrodynamic damping plates 20 are also known as "HEAVE PLATES" and are used to dampen the movements of the float under the effect of swell and wind. These plates in fact make it possible to increase the added mass of the float and its drag, to push the natural periods of the float as far as possible from the periods of the waves, in order to limit the excitation of the float and to dampen its movements as much as possible.

[0045] In the embodiment of Figure 5, it is provided to position two hydrodynamic damping plates 20 around each outer column 6 of the float. For each outer column, the two plates 20 are symmetrical with respect to a vertical plane P of symmetry of the pontoon 8.

[0046] Of course, it is possible to consider other shapes and positions for these hydrodynamic damping plates. For example, they could take the form of a disc placed under each outer column of the float.

[0047] Still in this embodiment, the hydrodynamic damping plates 20 each contain a watertight compartment 22 forming an additional ballast zone and the compartments 22 of the same external column are connected to each other by a network of additional pipes 24 coupled to the network of pumps 18.

[0048] Thus, in this embodiment, the control of the inclination of the float 2' is carried out by moving the ballast fluid between the compartments 14 of the pontoons but also by moving a ballast fluid between the compartments 22 of the different hydrodynamic damping plates 20.

Claims

Claims

1. Method for active and centralized ballasting of a semi-submersible float (2; 2') for an offshore wind turbine, the float comprising at least four columns including a central column (4) and three external columns (6) connected to the central column by lower branches forming pontoons (8), the pontoons (8) each being formed by an assembly of flat panels (81 to 8 4 ) and each presenting a polyhedral cross section, the flat panels (81 to 8 4) of each pontoon being assembled together at edges (10) which extend longitudinally between two columns and which are rounded by connecting at each of their longitudinal ends to a column by means of a transition piece (12), the method comprising the controlled and centralized movement of a ballast fluid between sealed compartments (14; 22) formed inside each pontoon (8) so as to be able to modify its inclination.

2. A method according to claim 1, wherein the movement of the ballast fluid is carried out between compartments (14) located inside a longitudinal end of each pontoon (8) on the outer column (6) side.

3. A method according to either of claims 1 and 2, further comprising moving a ballast fluid between additional sealed compartments (22) located at hydrodynamic damping plates (20) positioned around at least a portion of the outer columns (6).

4. Semi-submersible float (2; 2') for an offshore wind turbine with active and centralized ballasting, comprising at least four columns including a central column (4) and three external columns (6) connected to the central column by lower branches forming pontoons (8), the pontoons (8) each being formed by an assembly of flat panels (81 to 8 4 ) and each presenting a polyhedral cross section, the flat panels (81 to 8 4 ) of each pontoon being assembled together at the level of edges (10) which extend longitudinally between two columns and which are rounded in connecting at each of their longitudinal ends to a column via a transition piece (12), each pontoon comprising at least one sealed compartment (14; 22) forming a ballast zone, the float further comprising means (16, 18, 24) for moving a ballast fluid in a controlled and individual manner between the compartments of the float so as to be able to modify the inclination of the float.

5. A float according to claim 4, wherein each pontoon (8) comprises a compartment (14) located at a longitudinal end on the outer column side, the compartments being connected to each other by a network of pipes (16) coupled to a network of pumps (18).

6. A float according to one of claims 4 and 5, further comprising additional sealed compartments (22) located at hydrodynamic damping plates (20) positioned around at least a portion of each outer column (6), the additional compartments being connected to each other by a network of pipes (24) coupled to the network of pumps (18).

7. Float according to one of claims 5 and 6, in which the network of pumps (18) is positioned inside the central column (4) in the lower part thereof.

8. A float according to claim 4, wherein the outer columns (6) each have a cylindrical shape.

9. Float according to claim 4, in which the outer columns (6) are each formed by an assembly of flat panels and each have a polyhedral cross section.

10. A float according to any one of claims 4 to 9, wherein the central column (4) has a truncated cone shape.

11. A float according to any one of claims 4 to 9, wherein the central column (4) has a polyhedral shape.

12. An offshore wind turbine comprising a float according to any one of claims 4 to 11.

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